Ok, try this:
1) Highlight all the Best of Blondie tracks, right click, Get Info
2) Delete the artist name, which should be Blondie. If there is nothing in that box, that means that the Artist name must be slightly different in several of the tracks. If it is empty, type in Blondie and press OK.
This should edit it so they all have the same artist name, so should all appear in the same folder.
Hope that helps.
EDIT: Ah well, Shorty has sorted it a different way to me!